Magic technologies in need of handwavium in the OTU:
gravitics - may be used to explain away the maneuver drive, null grav modules, grav plates, acceleration compensation, repulsors and tractors, possibly heat sinks and a basis for jump drive discovery.
I have yet to see an explanation of how gravitics in the OTU is meant to work other than it is way beyond out understanding of physics.

The jump drive itself - and the higher TL versions such as the heironymus unit, the hop, skip and leap drives etc.
At least the idea of other dimensions is scientifically plausible.

Strong and Weak force manipulation - used to make nuclear dampers, meson guns and screens, disintegrators.

If we can generate a gravity field that pulls everything towards the deck at 1 G, then we can generate a gravity field forward at 1 G negating the perception of a 1 G acceleration of the ship (cf Einstein's Monkey).

Ishmael wrote: ↑
Only because Traveller has always ignored the square-cube law. Its the reason a Boeing 747 can't manoeuvre like a Zlin Acrobat.
( I really mean 'accelerate' as fast... not top speed )

There is no reason for a small craft to have higher acceleration than a large craft.
There is reason to believe that a small craft might rotate quicker (smaller dimensions, so lower moment of inertia for the same mass), hence change direction of acceleration.

Ishmael wrote: ↑
Only because Traveller has always ignored the square-cube law. Its the reason a Boeing 747 can't manoeuvre like a Zlin Acrobat.
( I really mean 'accelerate' as fast... not top speed )

There is no reason for a small craft to have higher acceleration than a large craft.
There is reason to believe that a small craft might rotate quicker (smaller dimensions, so lower moment of inertia for the same mass), hence change direction of acceleration.

Structural considerations, actually.
Consider doubling the size of a ship in each dimension... twice as long, tall, and thick,
mass increases eight-fold ( assuming ship density remains constant )
load bearing area of the structure increases only four-fold. The larger ship can only handle half the force, half the acceleration, of the smaller ship unless the larger ship increases the volume of its load bearing structure by nearly 3 times ( * 2.828 ) to make up the difference.
You'd also be providing 8 times the thrust through 4 times the area ( you'd have to increase the man. drive by nearly 3 times to keep the same level of thrust per unit area )

The square-cube law should also determine the number of hardpoints available to a ship as ship volume increases (assuming hardpoints scale with surface area).

But the skin of the hull (the armour) would only increase by four, offsetting the increased internal structure. By TNE, that modelled this (accurately or not), the big ship need less mass fraction for armour and structure.

Ishmael wrote: ↑
You'd also be providing 8 times the thrust through 4 times the area ( you'd have to increase the man. drive by nearly 3 times to keep the same level of thrust per unit area )

Again by TNE, this is not a significant problem, at least until the megaton range, since M-drives need very little surface area per thrust.

Ishmael wrote: ↑
The square-cube law should also determine the number of hardpoints available to a ship as ship volume increases (assuming hardpoints scale with surface area).

Agreed, and TNE did this by tracking surface area, not "hardpoints". But I have the impression that the level of detail in FFS wasn't universally appreciated.

One hardpoint per 100 Dt is a simple approximation, just as an M-drive of 1% of the ships volume produce 1 G acceleration, regardless of ship's current mass. Both are probably somewhat inaccurate, but simple to use.

But the skin of the hull (the armour) would only increase by four, offsetting the increased internal structure. By TNE, that modelled this (accurately or not), the big ship need less mass fraction for armour and structure.

The extra armor thickness is used as decks and bulkheads, given the scaled up distances between decks and bulkheads in the larger version. I can no longer check how FF&S1 did things, but if it was as you say, then it is wrong, and it would imply that as ship mass approaches infinity, then the mass ratio for load bearing structure approaches zero.
FF&S2 seems to be proper as far as it goes; I have no idea how it works with real-world structural strength of materials though.
Of, course, that is irrelevant to MongTrav rules, eh?

AnotherDilbert wrote:
Again by TNE, this is not a significant problem, at least until the megaton range, since M-drives need very little surface area per thrust.

I don't know about FF&S1 anymore, but FF&S2 requires .005m^2 per tonne of thrust, so you're probably right, as it means a type 'S' scout only needs 10m^2 for its thrusters by FFS2. But even then, doubling the scale of the type 'S' would mean 8 times the thruster area for the same performance even when the available area increase only 4-fold. This would eventually rob area needed for turrets, bays, sensors, etc.
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AnotherDilbert wrote:Agreed, and TNE did this by tracking surface area, not "hardpoints". But I have the impression that the level of detail in FFS wasn't universally appreciated.

One hardpoint per 100 Dt is a simple approximation, just as an M-drive of 1% of the ships volume produce 1 G acceleration, regardless of ship's current mass. Both are probably somewhat inaccurate, but simple to use.

I fully agree that keeping track of square meters of hull is cumbersome, and that tracking hardpoints is easier.
But area scales with volume^(2/3) and thus the number of hardpoints a ship may have should too, otherwise huge ships become vastly overgunned when compared to smaller ships, at rates that would allow a type 'S' to have a dozen turrets, if applied equally.
Personally, I use a 100dt cube as a baseline where it has ~600m^2 area. I say each 'hardpoint' uses 100m^2 for convenience. This gives a type 'S' 6 hardpoints. However, I also use hardpoints to mount thrusters, sensors and radiators ( 2 for thrusters, 2 for radiators, one for sensor and one for a turret, et al. ... I have not bothered to work out details ). This gives hardpoints = vol^(2/3) * .285
I know I am deviating from canon and rules, but I prefer my TU to be a little less space-opera-y.